The human eye includes a lens enclosed by a transparent capsule. Cataract is a condition characterized by opacity of the lens causing partial or total blindness. Cataracts are treated by removal of the defective lens and replacement with an artificial lens. An initial step of cataract surgery is an anterior capsulotomy, wherein an opening is made in the outer capsule to allow the removal of the defective lens.
The most common method of performing a capsulotomy is to rupture the capsule with a needle, in order to create a tear. The surgeon then grasps the free edge of the tear with either forceps or the needle and maneuvers, by manual dexterity, to create an approximately circular opening in the center of the capsule. Performing a capsulotomy with needle and forceps is difficult and the results are neither uniform nor predictable. This non-uniformity of the result is a disadvantage, because the success of the capsulotomy dictates to a large extent the quality and success of the entire cataract operation.
In order to access the capsule for the capsulotomy, an opening must be made in the cornea or sclera, which are layers of the eye external to the lens capsule. Fast recovery of the cornea or sclera is aided when the access opening has a minimal size. Therefore, the surgical manipulations of the capsulotomy are generally performed through an access wound in the cornea or sclera, which is expected to be no greater than 3.0 mm in length and 0.1 mm in height. Though the tissue in the cornea and sclera is somewhat distensible, it currently accommodates instruments no greater than 0.75 mm in height. As cataract surgery instrumentation advances, entrance wounds are being made smaller and smaller, in order to shorten the post operative recovery period.
U.S. Pat. No. 6,165,190 to Nguyen, the disclosure of which is incorporated herein by reference, describes a capsulectomy device having a needle that rotates up and down radially relative to the eye lens capsule, in order to cut the capsule. The needle is mounted on a rotating arm that controls the radius of the cut in the capsule. The radial rotation of the needle requires space, which may not be easily available in capsulectomy procedures.
U.S. Pat. No. 6,551,326 to Van Heugten et al., the disclosure of which is incorporated herein by reference, describes a capsulorrhexis device having a super elastic rod that is entered into the eye and formed into a circular loop with a desired radius. The rod cuts the eye lens capsule when it is retracted from the eye. This device may have problems of accurate operation and mechanical failure.
U.S. Pat. No. 6,629,980 to Eibschitz-Tsimhoni, the disclosure of which is incorporated herein by reference, describes an eye lens capsule cutting device having a curvilinear head portion. The force required by a physician in order to cut a hole in the capsule using such a cutting device is large, such that the physician is required to apply a substantial force in an accurate manner, in order to achieve the cutting, without cutting too deep into the eye and damaging the eye.
U.S. Pat. No. 6,066,138 to Sheffer et al., the disclosure of which is incorporated herein by reference, describes a medical instrument for burning a lens capsule of an eye.
U.S. Pat. No. 5,728,117 to Lash, the disclosure of which is incorporated herein by reference, describes a capsulorrhexis instrument that is retractable within a tube and extendable into a position projecting out of the tube. In the position out of the tube, the instrument has a circular shape with a sharp blade for cutting a hole in the capsule.